In the field of semiconductor technology, nano devices implemented by a bottom-up method based on nano synthesis and arrays have received much attention to overcome a current limitation in a process and to provide a new functionality.
Quantum dots having a zero-dimensional nano structure, and quantum wires, nanowires, or nanorods having a one-dimensional nano structure (hereinafter, the term “nanostructure” will be used as a common term for quantum wires, nanowires, nanorods, etc.) have been suggested as a nano material which can realize the possibility as described above
Currently, Si, Ge, an Al—Ga—In—P—N system, ZnO, SnO2, SiC, and the like are representative materials which have been widely studied domestically and abroad in order to form nanostructures such as semiconductor nanowires, nanorods, etc.
Particularly, zinc oxide (ZnO) which is a binary oxide semiconductor is a group 2-6 compound semiconductor having a wurzite structure, and is a typical N-type semiconducting material having a wide energy band gap of 3.37 eV and a high exciton binding energy of 60 meV. Further, zinc oxide (ZnO) has various production processes and structures, and is easily doped and has a narrow conduction band, and thus, the electrical-optical characteristics of zinc oxide are easily controlled according to a doping material. Accordingly, zinc oxide has received a spotlight as a suitable material for manufacturing a variety of devices such as optical instruments, optical devices, solar cells, light-emitting diodes (LEDs) and the like, and there are diverse studies on zinc oxide in progress.
Up to now, in the studies on zinc oxide, much research on zinc oxide (ZnO) nanostructures has been performed using various processes. Examples of main process methods include atomic layer deposition, pulsed laser deposition, molecular beam epitaxy, metal organic chemical vapor deposition, sputtering, spin coating, hydrothermal deposition, electrochemical deposition, etc.
In the above-described process methods, the electrochemical deposition method is a very simple method of growing zinc oxide (ZnO) nanostructures, allows zinc oxide nanostructures to be grown at a low temperature and can increase the area of a substrate, can be applied to a diversity of substrates, and can directly control the thicknesses of nanostructures, and the electrochemical deposition method has an advantage of a low initial cost. Most research on the electrochemical deposition method until now have been focused on conditions for growing zinc oxide nanostructures, that is, a growth temperature, an electric potential, a deposition time, whether a heat treatment is performed or not, whether a seed buffer layer is formed or not, and whether an additive is used or not.
Indium tin oxide (ITO) is a representative transparent electrode, and has been widely used for solar cells, smart glasses (i.e., electrochromic devices), flat panel displays, gas sensors, transparent displays, etc. Particularly, a structure in which zinc oxide (ZnO) nanorods are grafted on an ITO layer can be applied to optical devices, that is, to light-emitting diodes (LEDs), solar cells or the like, and many studies on the above-described structure are currently in progress.
However, although the research results of the attempts of vertical growth using a template such as anodic aluminum oxide (AAO) or the like, a buffer layer, and an additive to grow zinc oxide (ZnO) nanorods in a perpendicular direction on an ITO layer have been reported, these methods have a problem in that the optical characteristics of the zinc oxide (ZnO) nanorods generated by adding the buffer layer, additive or the like are degraded.